Careful design of the active cells in a power MOSFET device may provide for an increased breakdown voltage. However, the design of the active cells typically do not provide protection for localize portions of the device. Specifically, a device may be susceptible to failure because of the steep voltage gradient near the edges of the device. At the edge of the device the electric field needs to be reduced from the source potential to the drain potential in a smooth manner.
Prior art efforts to smoothly reduce the voltage gradient typically take up a relatively large amount of space near the edge of the device die. Attempts to use trench based termination structures to smoothly reduce the voltage to the drain potential requires multiple trenches to be formed near the edges of the die. The extra space needed for the termination region is space that active devices are not capable of being used for. The use of termination trenches also can render the outermost trench in the active area inactive. As such, even more space may be lost to the termination region. In addition to the extra space needed for multiple trenches, the trenches may also require additional processing steps. This could result in an increase of the cost of the devices. Therefore, there is a need in the art for a compact termination region that is capable of enabling the outermost trench to be a functioning trench as well.
It is within this context that embodiments of the present invention arise.